Displays are utilized in diverse applications for which visual information is presented. Displays include conference room projectors, optical equipment, operator displays, computer displays, dashboard displays, cockpit displays, entertainment displays, etc. In general, it is desirous to provide large gray scale capability to displays. Gray scale capability refers to the range from darkness to lightness for each pixel or element on a display. More gray scale capability (e.g., more bits of gray scale) are particularly important in avionic display systems, projection displays and other high-definition viewing applications.
In conventional display systems, such as, liquid crystal display (LCD) systems, the brightness of each pixel or element is controlled by a transistor. The display includes a matrix of transistors, such as, thin film transistors (TFTs) arranged in rows and columns. Alternatively, the display can include other light controlling or light emitting devices arranged in a matrix.
A column line is coupled to the drain or source associated with each transistor in each column. A row line is coupled to each gate associated with the transistors in each row. A row of transistors is activated by providing a gate control signal to the row line. The gate control signal turns on each transistor in the row. Each transistor in the row provides an analog voltage associated with its column line to cause the pixel or element to emit a particular amount of light.
Generally, a column driver circuit provides the analog voltage to the column lines so that the appropriate amount of light is emitted by each pixel or element. In conventional systems, the column driver circuit can typically provide approximately 8 or 16 levels of voltage at the column line (approximately 8 or 16 gray scale levels).
Conventional displays such as flat-panel displays, liquid crystal displays (LCDs) and projection light sources are not readily dimmable. Certain conventional displays have provided dimming modes by adjusting the amount of light emitted by a spacial light modulator by adjusting the light source. For conventional projection applications spacial light modulators can be of the type manufactured by Texas Instruments, such as, digital micromirror displays and digital light processors.
According to one type of conventional projection display, a conference room projector, the projector includes an arc lamp as its background or projection light source. The arc lamp is difficult to effectively dim. The power provided to the arc lamp is decreased to dim the display. However, reducing the power to the arc lamp can severely shorten the operational life of the arc lamp.
Further, conventional dimming schemes have not achieved a wide dimming range. Reducing the available gray scale range for the display when it is in the dimming mode is not an acceptable option for display customers.
There is a need for a display system or projection system including a dimming mode for some applications, such as avionics. Further still, there is a need for a display system or projection system including a dimming mode with does not compromise gray scale capabilities or lamp lifetime. Yet even further still, there is a need for a projection system or display system having a dimming mode which does not jeopardize the lifetime of background light sources.